One of the problems faced by the perfumery industry lies in the relatively rapid loss of the olfactive benefit provided by odoriferous compounds due to their volatility, particularly that of “top-notes”. This problem is generally tackled using a delivery system, e.g. capsules containing a perfume, to release the fragrance in a controlled manner.
Polyurea capsules, formed by polymerisation between a polyisocyanate and a polyamine, are well known in the art. In particular, polyurea microcapsules wherein guanidine is reacted with a polyisocyanate are known.
However, it would be desirable to provide capsules bearing high anionic charge both at acidic and basic pH. Such capsules would be advantageous over the known neutral capsules, because the presence of such charges would improve the dispersion of the capsules and their compatibility with anionic consumer product bases such as for example shower gels, shampoos and detergents. The charges would also enable the capsules to interact with cationic polymers, which facilitate deposition of capsules on substrates to which they are applied, such as human skin, hair or fabric. Good deposition of the capsules is particularly useful because it is correlated with good olfactive performance of the capsules and the long-lastingness of such performance over time.
The present invention addresses these problems. It has surprisingly been discovered that polyurea microcapsules having a wall made of the reaction product of a polyisocyanate with an amino acid and guanazole were highly negatively charged and that the replacement of known polyamines by guanazole improved the capsules deposition and olfactive performance.
To the best of our knowledge, no prior art document discloses core-shell polyurea microcapsules having a wall comprising the reaction product of a polyisocyanate with guanazole and an amino acid.
Reaction of amino acids and polyisocyanates for the formation of capsules is described in U.S. Pat. No. 5,304,448. However, such document is completely silent with regard to reacting the polyisocyanate also with guanazole.